The invention relates to wood impregnated with a resin, to a method for impregnating and preserving wood and to an impregnating composition.
It has been known to impregnate wood by applying oils, resins and waxes dissolved or emulgated in solvents onto the wood, whereas the solvents are removed thereafter. Such methods may be carried out at ambient or moderate temperature which largely prevents alterations of the impregnating agents. But the solvents have to be removed after the treatment, which is inefficient and raises disposal problems. Moreover, statutory provisions limit the application of such impregnation methods.
EP 891 244 B1 describes the impregnation of wood parts with a solvent-free melt of a natural resin, a wax or a mixture thereof by immersing the wood into the melt and treating the wood at elevated temperature, optionally at an excess pressure, for some time. It was observed that applying natural resins in this process at suitable temperatures and, in particular, during continuos or cyclic operation resulted in a not controllable discoloration of the melted natural resin which color even turned into black. Also the application of antioxidants or an inert gaseous atmosphere did not sufficiently prevent the discoloration, because most of the antioxidants are instable at the required process temperatures, are exhausted rapidly and, therefore, cannot efficiently be employed. Further the application of inert gases is counteracted by the oxygen which is introduced into the process by the porous wood in any case.
Because of the autocatalytic oxidation of natural resins or natural resin acids respectively, which starts at ambient temperature and intensifies with increasing temperature, the melt of natural resins becomes rapidly unsightly due to the discoloration from brown to black. This deters the application of natural resins for impregnating decorative or visible pieces and parts, e.g. floorings, furniture, window frames, wooden fronts, parts of wooden facedes, etc.
One object of the invention is to provide an impregnating composition based on a solvent-free resin melt which keeps a light color if applied at elevated temperature and pressure. The light color should be largely maintained during a series of loading cycles.
Another object of the invention is to provide wood and wooden pieces impregnated with a resin melt having on the whole a nearly unchanged color after the loading treatment. In particular, an object is to provide light colored wood or wood parts impregnated with a resin melt.
A further object of the invention is to suppress the leaking of the impregnated wood at least up to 85xc2x0 C. Surfaces of front parts and window frames which are exposed to solar radiation may be heated to 85xc2x0 C., locally even to 90xc2x0 C., in particular if they are dark colored, for instance by a dark varnish or a dark colored wood type.
Another object of the invention is to provide a method for impregnating wood with a solvent-free resin melt.
Other objects and advantages of the present invention will become apparent from the following detailed description.
According to the invention wood is impregnated with a solvent-free melt of a modified natural resin, a modified natural resin acid and/or a terpene resin. Besides the modified natural resin and/or modified natural resin acid, melts according to the invention may comprise wax and further additives.
Melts composed of modified natural resins resp. modified natural resin acids according to the invention do not tend to discolor even at the given temperatures of the loading treatment so that the wood treated with a melt according to the invention mainly retains its natural Nuance in color. Because of its resistance against discoloration, the impregnating melt according to the invention may be used for a series of loading cycles and for a prolonged period. Further advantages of modified natural resins and/or modified natural resin acids according to the invention are, firstly, that they do not tend to crystallize from their melt, because crystalline natural resin shows distinct brittleness, and, secondly, have a certain resistance against ultra-violet radiation.